Device for delivery of multiple liquid sample streams to a mass spectrometer

ABSTRACT

An electrospray apparatus employing multiple electrospray needles mounted on a rotatable plate sequentially delivers multiple sample streams to a mass spectrometer for analysis. The electrospray device includes an electrospray chamber, a rotatable needle supporting plate, a plurality of electrospray needles mounted on the plate, and a charger for applying a charge to droplets delivered to the electrospray chamber by the needles. The rotatable electrospray apparatus provides fast repetitive screening of simultaneously operating chromatography columns with a single mass spectrometer.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The invention relates to liquid delivery devices, and moreparticularly, the invention relates to devices for delivery of multipleliquid sample streams to a S mass spectrometer for screening of compoundlibraries.

[0003] 2. Brief Description of the Related Art

[0004] In recent years, a large number of combinatory chemistrytechniques have been developed which permit vast libraries of diversechemical compounds to be rapidly synthesized. In combinatory chemistry,a series of chemical reactions is conducted, typically employing aplurality of reagents at each step, to generate a library of compounds.Such techniques have the potential to greatly accelerate the discoveryof new compounds having biologically useful properties by providinglarge collections of diverse chemical compounds for biologicalscreening.

[0005] Mass spectrometry is emerging as an important tool for theinterrogation of combinatorial libraries. To date, mass spectrometry hasbeen used to assess library quality and, when coupled with molecularrecognition technologies, has allowed for some success in the isolationand characterization of active library compounds. Applications of massspectrometry have become increasingly important in combinatory chemistryand biological research.

[0006] Mass spectrometry obtains molecular weight and structuralinformation on chemical compounds by ionizing the molecules andmeasuring either their time-of-flight or the response of the moleculartrajectories to electric and/or magnetic fields. The electrosprayprocess is one of the most promising techniques for producing gas phasemolecular ions for a wide range of molecular entities.

[0007] According to a conventional electrospray process, a samplesolution containing molecules of interest and a suitable solvent ispumped or drawn through an electrospray needle into an electrospraychamber. A potential of up to several kilovolts may be applied to theneedle to generate a fine spray of charged droplets. Conversely, theneedle may be held at ground and the solution sprayed into an externallygenerated electric field. The droplets are typically sprayed into thechamber at atmospheric pressure. Optionally, this chamber houses gaslines (e.g., N₂) to aid in the nebulization of the solvent stream andthe disolvation or evaporation of solvent. The ions generated by theelectrospray process are then guided into the mass spectrometer byappropriate electric field gradients. This typically requires multiplestages of pumping for the removal of excess neutrals, such as solventvapor.

[0008] With this conventional electrospray apparatus, the electrosprayneedle is connected to a single sample stream and delivers the moleculescontained therein by the electrospray process to the mass spectrometerfor analysis. When multiple sample streams are prepared, it is timeconsuming to switch between successive sample streams. This is due tothe fact that the available electrospray mass spectrometers are marketedwith a single electrospray needle. Therefore, switching streams involvesphysically breaking the connection between the needle and one samplestream, and re-establishing a connection with the next stream. Asidefrom the time involved in switching streams, the possibility exists forcross-contamination of the various streams.

[0009] It would be desirable to permit multiple sample streams frommultiple chromatography columns or from other sample sources to beeasily connected to the electrospray apparatus of a mass spectrometerfor intermittent analysis of the sample streams from multiple columns.It would also be desirable to automatically move from analysis of onesample stream to another to analyze a plurality of sample streams in asshort a period of time as possible.

SUMMARY OF THE INVENTION

[0010] The present invention relates to an electrospray apparatusemploying multiple electrospray needles mounted on a rotatable plate tosequentially deliver multiple sample streams to a mass spectrometer foranalysis.

[0011] In accordance with one aspect of the invention, an electrospraydevice for a mass spectrometer includes an electrospray chamber, arotatable needle support, a plurality of electrospray needles mounted onthe rotatable needle support, and a charger. The electrospray needlesare connectable to a plurality of sample streams for delivery ofdroplets of one of the sample streams at a time to a mass spectrometerorifice of the electrospray chamber. The charger applies a charge to thedroplets of the sample stream in the electrospray chamber and causes thedroplets to be focused into a beam passing through the orifice into themass spectrometer.

[0012] In accordance with another aspect of the present invention, amethod is provided for delivering a plurality of sample streams to amass spectrometer for analysis. The method includes the steps of:providing a plurality of sample streams to a plurality of electrosprayneedles mounted on a rotating plate; continuously spraying the samplestreams with the electrospray needles; and sequentially positioning anoutlet of each of the electrospray needles at delivery position for apredetermined dwell time by rotating and stopping the plate to deliverthe sample streams to the mass spectrometer.

BRIEF DESCRIPTION OF THE DRAWINGS

[0013] The invention will now be described in greater detail withreference to the preferred embodiments illustrated in the accompanyingdrawings, in which like elements bear like reference numerals, andwherein:

[0014]FIG. 1 is side view of a multiple needle electrospray apparatusfor delivery of sample streams to a mass spectrometer;

[0015]FIG. 2 is a top view of the multiple needle electrospray apparatusof FIG. 1; and

[0016]FIG. 3 is a schematic top view of an alternative embodiment of amultiple needle electrospray apparatus.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0017] A multiple needle electrospray apparatus for a mass spectrometerincludes a plurality of electrospray needles 10 mounted on a rotatableplate 12 for sequential injection of multiple sample streams. Therotatable electrospray apparatus allows collection of data from multiplesample streams by a single mass spectrometer 20 in a short time byrotating the electrospray apparatus to sequentially monitor the streamfrom each of the needles 10 for a brief duration before rotating theplate 12 to another of the needles.

[0018] One example of a method for screening compound libraries whichinvolves analysis of multiple sample streams by electrospray massspectrometry is described in U.S. patent application Ser. No. _______,filed on even date herewith (Attorney Docket No. 026579-174), which isincorporated herein by reference in its entirety. According to oneapplication of this method, a compound library is prepared, such as bycombinatorial chemistry techniques. Multiple sample streams each ofwhich contain a compound library or sublibrary are passed through aplurality of frontal chromatography columns. Each stream being passedthrough a single column to analyze the interaction of members of thatsample stream with a target receptor within the column. The columnsinclude a solid support or inert material on which the target receptoris bound or coupled. As the sample stream is continuously infusedthrough the chromatography column, those compounds within the samplestream having a higher affinity for the target receptor (i.e., ligands)will be more strongly bound to the target receptors. When substantiallyall of the target receptors are filled, the compounds will break throughand begin to pass out of the column with those compounds having thelowest affinity passing out of the column first. The sample streamsexiting the chromatography columns are analyzed by electrospray massspectrometry to determine the break through time for each compound. Massspectrometry is particularly useful for this process because it allowsfor both detection and identification of the library members present inthe sample streams exiting the columns.

[0019]FIG. 1 illustrates a first embodiment of an electrospray devicefor delivery of multiple liquid sample streams to the mass spectrometer20. The electrospray device includes an electrospray chamber 14 forcharging the droplets of a sample stream delivered by the electrosprayneedles 10 and delivering the charged ions in a beam to the massspectrometer 20.

[0020] The electrospray needles 10 each have an upper end mounted on therotatable plate 12 in the circular arrangement illustrated in the topview of FIG. 2. The lower ends of the electrospray needles may berotated into a reproducible delivery position within the electrospraychamber 14. The delivery position is at a precise location with respectto an orifice 22 of the mass spectrometer 20 which allows the sprayeddroplets to be focused into a beam passing through the orifice. Thedelivery position is preferably within about ±0.5 mm of an idealposition. In fluid connection with each of the electrospray needles 10is a sample source such as the chromatography columns 18 illustrated inFIG. 1. The chromatography columns 18 are preferably mounted on the topof the rotatable plate 12.

[0021] The electrospray chamber 14 surrounds the orifice 22 of the massspectrometer and is open to atmospheric pressure. The electrospraychamber 14 includes a front wall 28 having two vertically extendingslots 30 which allow the electrospray needles 10 to pass into and out ofthe electrospray chamber as the plate 12 is rotated. As illustrated inthe top view of FIG. 2, a top wall 32 of the electrospray chamber 14includes a semicircular opening 34 which receives a portion of therotatable plate 12.

[0022] The electrospray needles 10 are preferably coaxial needles whichdeliver the sample stream through an inner needle lumen and deliver anebulizer gas, such as nitrogen, coaxially around the sample stream tobreak up the flow of the sample stream into a spray of droplets. Theelectrospray chamber 14 includes a charged sampling plate 16 surroundingthe mass spectrometer entry orifice 22. The electrospray chamber 14 alsoincludes an electrode 26 in the form of a half cylindrical portion ofthe front wall 28 of the electrospray chamber. The charged samplingplate 16 and the half cylindrical electrode 26 are charged with anelectric potential preferably of about 0 to 6000 volts. The electricfield established by the sampling plate 16 and the electrode 26surrounds the grounded needle 10 and imparts a charge to the sprayeddroplets.

[0023] According to an alternative embodiment of the invention, thecharging of the sample stream droplets exiting the electrospray needle10 may be accomplished by use of a charged electrospray needle in placeof the charged sampling plate 16 and electrode 26. The needle 10 may becontinuously charged or may be charged only when the needle reaches thedelivery position within the electrospray chamber 14 by an electricalcontact.

[0024] A counter current drying gas, such as nitrogen, is delivered tothe electrospray chamber 14 through a passageway 24 between the chargedsampling plate 16 and the entry orifice 22 to assist in desolvating orevaporating the solvent from the sample stream to create fine droplets.According to an alternative embodiment of the invention, the drying gasmay be delivered to the electrospray chamber 14 in manners other thanthrough the passageway 24. In addition, the nebulizer gas may bedelivered to the electrospray chamber 14 separately rather than by aco-axial flow through the electrospray needle. Both the nebulizer gasand the drying gas are introduced into the electrospray chamber 14 toobtain fine droplets of the sample stream. However, depending on theflow rate of the sample stream, the fine droplet size may be achievedwithout the need for a nebulizer gas and/or a drying gas.

[0025] The rotatable plate 12 is rotated by a motor connected to a driveshaft 36 of the plate. Preferably the motor is interfaced with acontroller to control the rotation of the plate and the dwell times foreach of the needles. Although the rotatable plate 12 has beenillustrated as a circular plate, it should be understood that otherplate shapes, such as multi-sided plates, rings, and the like, may beused without departing from the invention.

[0026] In operation, multiple sample streams are continuously deliveredto each of the chromatography columns 18 from sample sources by, forexample, a pump, such as a syringe pump. The sample streams exiting thecolumns 18 may be combined with a diluent in a mixing chamber or mixingtee 38 positioned between the column and the needle 10. The samplestreams pass continuously through the electrospray needles 10 with anebulizer gas delivered around the sample streams to break up the flowinto droplets. Sample streams pass through all of the needles 10simultaneously with only one of the streams from a needle positioned atthe delivery position being analyzed by the mass spectrometer at a time.The sample streams from the remaining needles 10 are collected by a tray40 for delivery to waste or for reuse.

[0027] To perform analysis of the multiple sample streams, oneembodiment of the invention provides that the rotatable plate 12 isstepped in one direction, e.g., counter clockwise, through approximatelyhalf of the needles 10. When a quadrupole mass spectrometer is used adwell time for each electrospray needle 10 ranges from about 0.5 to 10seconds, preferably about 1 to 5 seconds before switching to the nextcolumn. After analysis of approximately half the sample streams, therotatable plate 12 then returns clockwise to a home position and beginsstepping in an opposite direction, e.g., clockwise, through theremaining half of the needles 10. Finally, the rotatable plate 12returns again to the home position and repeats the procedure. The systemoperates continuously for a preset period of time related to thechromatographic requirements. Step times for rotation between successiveneedles is preferably about 10 to 100 msec. The rotation of the plate 12in one direction followed by reversing the rotation is preferred toprevent the feed lines for feeding the sample streams from the pump tothe columns 18 from becoming twisted.

[0028] According to an alternative embodiment of the invention, thesample source, the pump or alternative, and the feed lines for deliveryof the sample streams to the columns 18 may be mounted on the plate 12.With this embodiment, the plate 12 will be rotated continuously in onedirection to sequentially analyze the flows from each of the needleswithout requiring the plate to reverse direction and return to a homeposition.

[0029] The mass spectrometer for use with the present invention may beany of the known mass spectrometers including a quadrupole massspectrometer, quadrupole ion trap mass spectrometer, Penning or Paul iontrap mass spectrometer, FTICR (Fourier transform inductively coupledresonance) mass spectrometer, time-of-flight mass spectrometer, and thelike. A time-of-flight mass spectrometer is preferred due to its highspectral acquisition rate (>100 spectra per second). However, the slowerquadrupole mass spectrometer may also be used which can record spectraat a rate of approximately 0.5 to 1 per second. The dwell times foranalysis of each sample stream will vary depending on the spectralacquisition of the mass spectrometer used.

[0030]FIGS. 1 and 2 illustrate an electrospray device for analysis ofsample streams from ten columns. When the electrospray device having tencolumns is employed with a quadrupole mass spectrometer with analysis ata rate of about 1 spectrum per second and a dwell time of about 5seconds per column is used, the system will take about 5 spectra fromeach column at a time and will cycle through all the columns inapproximately 60 seconds.

[0031] Alternative embodiments of the invention may include differentnumbers of electrospray needles depending on the number of samplestreams which are to be analyzed. The spacing of the multipleelectrospray needles 10 is important to the operation of theelectrospray device. In particular, the electrospray needles 10 shouldbe spaced sufficiently to prevent cross over effects resulting from thesample stream from one columns influencing the analysis of the samplestream of an adjacent column. In addition, the electrospray needles 10should be spaced as close together as possible to minimize the steptimes for rotation between adjacent needles. Preferably, the spacingbetween columns should be about 0.5 cm to 10 cm, depending on the massspectrometer used.

[0032]FIG. 3 is a top view of an alternative embodiment of a rotatableelectrospray apparatus for delivery of sample streams to a massspectrometer 120. The electrospray apparatus includes a plurality ofelectrospray needles 110 mounted in a radial arrangement on a rotatableplate 112. Each of the needles 110 are in fluid connection with achromatography column 118. The radial arrangement of the electrosprayneedles 110 allows more columns 118 to be positioned on a rotatableplate 112 of a smaller diameter. According to this embodiment, thedischarge ends of the needles 110 are preferably spaced a distancesufficient to prevent a cross over effect between adjacent needles.However, the columns 118 can be arranged close together around theperiphery of the rotatable plate 112.

[0033] The orientation and arrangement of the rotatable plate 12, thecolumns 18, and the electrospray needles 10 may be varied to achievemany different angular relationships for use with different types ofmass spectrometers. For example, the rotatable plate 12 may bepositioned vertically and the columns 18 and needles 10 may bepositioned horizontally. In addition, for some types of massspectrometers the electrospray chamber is not enclosed by walls.

[0034] The present invention provides distinct advantages over prior artmethods of operating and screening one column at a time. The rotatableelectrospray apparatus allows multiple sample streams to be easilydelivered to a single mass spectrometer and provides fast repetitivescreening of simultaneously operating columns with a single massspectrometer.

[0035] While the invention has been described in detail with referenceto the preferred embodiments thereof, it will be apparent to one skilledin the art that various changes and modifications can be made andequivalents employed, without departing from the present invention.

What is claimed is:
 1. An electrospray device for a mass spectrometercomprising: an electrospray chamber; a rotatable needle support; aplurality of electrospray needles mounted on the rotatable needlesupport, the electrospray needles connectable to a plurality of samplestreams for delivery of droplets of one of the sample streams at a timeto a mass spectrometer orifice of the electrospray chamber; and acharger for applying a charge to the droplets of the sample stream inthe electrospray chamber and causing ions to be focused into a beampassing through the orifice into the mass spectrometer.
 2. Theelectrospray device according to claim 1 , wherein the rotatable needlesupport is a rotatable disk having the plurality of electrospray needlesmounted in a substantially circular parallel arrangement on the disk. 3.The electrospray device according to claim 1 , wherein the rotatableneedle support is a rotatable disk having the plurality of electrosprayneedles mounted in a radial arrangement on the disk.
 4. The electrospraydevice according to claim 1 , wherein the plurality of electrosprayneedles are coaxial needles having an inner lumen for delivery of thesample stream and an outer lumen for delivery of a nebulizer gas.
 5. Theelectrospray device according to claim 1 , wherein the charger comprisesa charged sampling plate positioned within the electrospray chambersubstantially surrounding the mass spectrometer orifice and an electrodepositioned on an opposite side of the electrospray needle from thecharged sampling plate.
 6. The electrospray device according to claim 1, wherein the charger comprises an electrical contact for electricallycharging the electrospray needles by connection to a voltage source. 7.The electrospray device according to claim 1 , wherein the electrospraychamber includes a chamber wall having slots for allowing theelectrospray needles to pass into and out of the electrospray chamber.8. The electrospray device according to claim 1 , further comprising aplurality of chromatography columns mounted on the rotatable needlesupport, wherein each of the chromatography columns is in fluidconnection to one of the electrospray needles for delivery of the samplestreams exiting the chromatography columns to the mass spectrometer. 9.The electrospray device according to claim 1 , further comprising amotor for rotation of the rotatable needle support and a controller forcontrolling the rotation of the needle support to achieve a consistentdwell time for each of the electrospray needles.
 10. The electrospraydevice according to claim 9 , wherein the controller rotates the needlesupport in a first direction to analyze the sample streams fromapproximately one half to the electrospray needles and rotates theneedle support in a second direction to analyze the sample streams froma remaining approximately one-half of the electrospray needles.
 11. Amethod of delivering a plurality of sample streams to a massspectrometer for sequential analysis, the method comprising: providing aplurality of sample streams to a plurality of electrospray needlesmounted on a rotating plate; continuously spraying the sample streamswith the electrospray needles; and sequentially positioning an outlet ofeach of the electrospray needles at delivery position for apredetermined dwell time by rotating and stopping the plate to deliverthe sample streams to the mass spectrometer.
 12. The method according toclaim 11 , wherein the predetermined dwell time is about 0.5 to 10seconds.
 13. The method according to claim 11 , wherein the plate isrotated in a first direction to sequentially deliver a plurality issample streams to the mass spectrometer and the plate is then rotated ina second direction.
 14. The method according to claim 11 , wherein theelectrospray needles which are not positioned at the delivery positiondeliver the sample streams to a collection tray.